The invention relates to a jetting head capable of ejecting various kinds of liquid in the form of droplets for use in an ink jet printer, a display manufacturing apparatus, an electrode forming apparatus, a biochip manufacturing apparatus, etc., and more particularly, to a jetting apparatus having a plurality of flexible flat cables to be used for supplying drive signals from a head driver to a jetting head.
As a jetting apparatus having a jetting head capable of ejecting liquid in the form of a liquid droplet, for example, there has been proposed an ink jet printer in which ink droplets are ejected to record an image or the like on recording paper, an electrode forming apparatus in which an electrode material in a liquid form is ejected onto a substrate to thereby form electrodes, a biochip manufacturing apparatus in which biological samples are ejected to manufacture biochips, or a micropipette for ejecting a predetermined amount of a sample into a vessel.
For instance, in an ink jet printer employing piezoelectric elements as drive elements for ejecting ink, a plurality of piezoelectric elements, which are provided so as to correspond to a plurality of nozzles of a print head, are selectively activated, whereby ink droplets are ejected from the nozzles in accordance with the dynamic pressure generated by the respective piezoelectric elements. Dots are formed on recording paper by causing the ink droplets to adhere to the recording paper, thus effecting printing operation.
Here, the piezoelectric elements are provided so as to correspond to nozzles to be used for ejecting ink droplets. The piezoelectric elements are actuated by a drive signal supplied from a head driver mounted in the print head, thereby ejecting ink droplets.
It is therefore an object of the invention to provide a device and a method for driving a jetting head designed to readily retain predetermined bias voltages of respective piezoelectric elements through use of a simple, compact configuration and at low cost.
In order to achieve the above object, according to the invention, there is provided a head driving device, which drives a plurality of pressure generating elements for generating pressure fluctuation in a jetted object contained in each of associated pressure chambers formed in a jetting head of a jetting apparatus to eject the jetted object from each of nozzles communicated with the associated pressure chambers, the head driving device comprising:
a head driver, which generates a drive signal which is selectively applied to at least one of the pressure generating elements to be driven; and
a bias potential provider, which selectively applies a bias potential to at least one of the pressure generating elements not to be driven.
In such a configuration, the non-actuated pressure generating elements are held at the bias potential. Accordingly, the voltage applied to both electrodes of the non-actuated pressure generating elements becomes substantially zero. Hence, power draw is reduced, and a voltage drop stemming from spontaneous discharge of the pressure generating elements becomes smaller. Hence, a power loss is diminished.
Further, occurrence of discharge due to a potential difference between pressure generating elements to be driven and pressure generating elements not to be driven is also reduced. In addition, a further increase in arrangement density of a head can be attained without involvement of an operation for providing insulation between the electrodes of the pressure generating elements.
Preferably, the bias potential is a reference potential of the drive signal.
Preferably, the bias potential provider includes a potential applier which applies the bias potential, and a charger which charges the potential applier with a drive potential of the drive signal.
Here, it is preferable that the charger includes a transistor which applies the drive potential to the potential applier, and a switcher which supplies the drive signal to a base terminal of the transistor during a time period in which the drive signal deactivates the pressure generating elements.
In such a configuration, the transistor is turned on by the supplied drive signal to charge the potential applier with the bias potential.
Here, it is further preferable that the switcher continuously supplies the drive signal before and after a jetting operation is performed.
Specifically, the drive signal is supplied to discharge the potential applier after the jetting operation is performed.
Before the jetting operation, since the potential applier is gradually charged to reach the bias potential by the continuous supply of the drive signal, there is prevented occurrence of faulty operations of respective pressure generating elements, which would otherwise be caused by a sudden increase in the potential of the ground-side electrodes before commencement of the jetting operation.
After the jetting operation, since the potential applier is gradually discharged by the continuous supply of the drive signal, there is prevented occurrence of faulty operations of the respective pressure generating elements, which would otherwise be caused by a sudden drop in the voltage of the ground-side electrodes after completion of the jetting operation.
Further, it is preferable that: the head driver is mounted on the jetting head, and the switcher is embodied by a part of a switching circuit included in the head driver which selectively applies the drive signal to the at least one pressure generating elements to be driven.
In such a configuration, the switcher is provided by utilizing a surplus unused section of an existing switching circuit of the head driver mounted on a jetting head, thereby curtailing the cost of parts. Further, a space to be used for mounting the switcher is not particularly required, thus rendering the apparatus compact.
According to the invention, there is also provided a method of driving a jetting head provided with pressure generating elements, the method comprising steps of:
generating a drive signal selectively applied to at least one of the pressure generating elements to be driven to eject jetted objects; and
applying a bias potential from a potential applier to at least one of the pressure generating elements not to be driven.
Preferably, the driving method further comprises a step of charging the potential applier with a drive potential of the drive signal.
Here, it is preferable that the charging step is performed during a time period in which the drive signal deactivates the pressure generating elements.
It is further preferable that the charging step is performed during a time period in which the drive signal deactivates the pressure generating elements.
According to the invention, there is also provided a head driving device, which drives a plurality of pressure generating elements for generating pressure fluctuation in a jetted object contained in each of associated pressure chambers formed in a jetting head of a jetting apparatus to eject the jetted object from each of nozzles communicated with the associated pressure chambers, the head driving device comprising:
a head driver, which generates a drive signal which is selectively applied to at least one of the pressure generating elements to be driven;
a bias potential provider, which applies a bias potential to respective ground-side electrodes of the pressure generating elements; and
an IC package, in which the head driver and the bias potential provider are provided.
In such a configuration, the ground-side electrodes of the pressure generating elements are held at the bias potential.
Accordingly, the voltage to be applied across both electrodes of the pressure generating elements is reduced. Therefore, power consumption is diminished, and a voltage drop stemming from spontaneous discharge of the pressure generating elements is small, thereby reducing a power loss.
Further, since the voltage to be applied to the pressure generating elements becomes relatively low, electric discharge stemming from a voltage difference between pressure generating elements to be driven and pressure generating elements not to be driven is also reduced. In addition, a further increase in arrangement density of the pressure generating elements can be attained without involvement of an operation for providing insulation between the electrodes of the pressure generating elements, even when pressure generating elements eventually assume a lower withstand voltage.
Since the head driver and the bias potential provider are provided integrally within an IC package, a reduction in packing, wiring, and connection space can be attained.
Preferably, the bias potential is a reference potential of the drive signal.
In such a configuration, the voltage applied to across electrodes of the pressure generating elements becomes substantially zero. Hence, a voltage drop stemming from spontaneous discharge of the pressure generating elements becomes smaller, thereby reducing a power loss.
Preferably, the head driving device further comprising:
a capacitor, having a capacitance which is sufficiently greater than a total electrostatic capacitance of the pressure generating elements, the capacitor provided with a first terminal which is electrically connected to the ground-side electrodes and a second terminal which is grounded; and
a control resistor, which electrically connects the first terminal of the capacitor and the bias potential provider.
In such a configuration, the capacitor is charged with a bias potential output from the bias potential provider by way of the control resistor. In a case where an amplifier is provided in the bias potential provider, since the charging voltage of the capacitor is applied to the pressure generating elements, it is not necessary to provide an amplifier of a high speed operable type. A low-speed, small-capacity amplifier can be used, thereby curtailing cost of such an amplifier.
Due to the existence of the control resistor, the charging and discharged currents substantially do not flow into the amplifier of the bias potential provider, but flow into the condenser. Hence, the amount of heat dissipated by the amplifier is reduced.
Here, it is preferable that the bias potential provider charges the capacitor with a potential according to a data signal inputted to the bias potential provider, so that the charged potential is applied to the ground-side electrodes of the pressure generating elements as the bias potential.
Further, it is preferable that the bias potential provider discharges the capacitor according to a data signal inputted to the bias potential provider, so that the ground-side electrodes of the pressure generating elements are discharged.
In such a configuration, due to the existence of the control resistor, a large discharged electric current does not flow into the bias potential provider, thereby lowering the amount of heat dissipated by e.g., an amplifier of the bias potential provider.
Further, it is preferable that the data signal is inputted to the head driver to generate the drive signal.
In such a configuration, a data signal can be input from a common connection terminal of an IC package constituting the head driver and the bias potential provider. Accordingly, inputting a data signal individually to the head driver and to the bias potential provider is not required, thereby reducing the wiring and connection space.
Further, it is preferable that the head driving device further comprises a temperature detector, which detects a temperature of the jetting head. The data signal corresponds to the bias potential which is determined by the detected temperature.
Alternatively, it is preferable that the number of bits forming the data signal is less than the number of a signal inputted to the head driver to generate the drive signal.
The setting accuracy of the bias potential output from the bias potential provider may be lower than the drive signal of the head driver. In such a case, a D/A converter to be incorporated in the bias potential provider can be embodied by a more compact and less-expensive D/A converter.